In recent years, developments have been actively carried out for vacuum ultraviolet ray excitation type light-emitting elements in which phosphors are excited by ultraviolet rays radiated by electric discharge of a rare gas, to emit lights. One example thereof is a plasma display panel (hereinafter referred to as "PDP"). PDP is one wherein narrow discharge spaces (hereinafter referred to as "cells") are arranged in a matrix form. Each cell is provided with an electrode, and the inside of each cell is coated with a phosphor. In each cell, a rare gas such as Xe or Xe-Ne is sealed in. When an electric energy is applied from the electrode, discharge of the rare gas takes place in the cell, whereby vacuum ultraviolet rays are radiated, and the phosphor coated in the cell is thereby excited to emit visible lights. By arranging such cells, an image can be displayed by lights emitted from the respective cells. Full color display can be carried out by arranging cells coated with phosphors which emit red, blue and green colors in a matrix form. This is full color PDP.
Full color PDP is practically used in which (Y, Gd)BO.sub.3 :Eu is used as a red color phosphor, Zn.sub.2 SiO.sub.4 :Mn as a green color phosphor and BaMgAl.sub.14 O.sub.23 :Eu as a blue color phosphor (separate volume of Nikkei Micro Device Journal, "Flat Panel Display", 1994, published by Nikkei BP Company).
As a green phosphor to be excited with vacuum ultraviolet rays, in addition to the above mentioned Zn.sub.2 SiO.sub.4 :Mn, Mn-activated alkaline earth aluminate phosphors BaAl.sub.12 O.sub.19 :Mn and BaMgAl.sub.14 O.sub.23 :Mn, are known as ones capable of emitting lights highly efficiently (e.g. "Phosphor Handbook", compiled by Phosphor Research Society, p. 330-335, published by Ohm Company).
Further, JP-A-52-143987 discloses an ultraviolet ray excitation type light-emitting element employing Ba.sub.0.9 Mn.sub.0.16 Al.sub.2 O.sub.3 or Ba.sub.0.3 Mg.sub.0.6 Mn.sub.0.1 .multidot.8Al.sub.2 O.sub.3. However, in order to improve the properties of full color PDP, it is desired to further improve the properties, such as emission efficiency, of the phosphor to be used here.
Accordingly, the present invention is intended to provide a phosphor having luminance improved for vacuum ultraviolet ray excitation and a process for its production, as well as vacuum ultraviolet ray excitation type light-emitting element with high luminance.